require 'concurrent/map' require 'openssl' module ActiveSupport # KeyGenerator is a simple wrapper around OpenSSL's implementation of PBKDF2. # It can be used to derive a number of keys for various purposes from a given secret. # This lets Rails applications have a single secure secret, but avoid reusing that # key in multiple incompatible contexts. class KeyGenerator def initialize(secret, options = {}) @secret = secret # The default iterations are higher than required for our key derivation uses # on the off chance someone uses this for password storage @iterations = options[:iterations] || 2**16 end # Returns a derived key suitable for use. The default key_size is chosen # to be compatible with the acceptable key length of aes-256-cbc, the default cipher. def generate_key(salt, key_size=32) OpenSSL::PKCS5.pbkdf2_hmac_sha1(@secret, salt, @iterations, key_size) end end # CachingKeyGenerator is a wrapper around KeyGenerator which allows users to avoid # re-executing the key generation process when it's called using the same salt and # key_size. class CachingKeyGenerator def initialize(key_generator) @key_generator = key_generator @cache_keys = Concurrent::Map.new end # Returns a derived key suitable for use. The default key_size is chosen # to be compatible with the acceptable key length of aes-256-cbc, the default cipher. def generate_key(salt, key_size=32) @cache_keys["#{salt}#{key_size}"] ||= @key_generator.generate_key(salt, key_size) end end class LegacyKeyGenerator # :nodoc: SECRET_MIN_LENGTH = 30 # Characters def initialize(secret) ensure_secret_secure(secret) @secret = secret end def generate_key(salt) @secret end private # To prevent users from using something insecure like "Password" we make sure that the # secret they've provided is at least 30 characters in length. def ensure_secret_secure(secret) if secret.blank? raise ArgumentError, "A secret is required to generate an integrity hash " \ "for cookie session data. Set a secret_key_base of at least " \ "#{SECRET_MIN_LENGTH} characters in config/secrets.yml." end if secret.length < SECRET_MIN_LENGTH raise ArgumentError, "Secret should be something secure, " \ "like \"#{SecureRandom.hex(16)}\". The value you " \ "provided, \"#{secret}\", is shorter than the minimum length " \ "of #{SECRET_MIN_LENGTH} characters." end end end end